Any art that is done on an ephemeral item such as a napkin
or paper table cloth. Often left behind with the check at modest restaurants, napkinart can have surprising value.
There's a story told in the movie, "The Paper," about journalists celebrating the Olympics in Spain. When the bill comes, it is far too much to afford, but a little old man sitting in the corner signals the waiter and then scribbles something on a napkin. That napkin pays the bill because the little old man was Picasso!
Then there's the true story of Basquiat, whose career as an
artist was brief but bright, as he died very young. He was known to dash off his creations on such things a matchbooks,
and they went for thousands of dollars. These, too would
be considered napkinart.

The waitperson was surprised and delighted to find a colorfulnapkinart pieceleft along with payment for the bill.